This invention relates to a windshield wiper device used for wiping rainwater, snow, mud, dust or any other dirt off the window glass of a vehicle such as automobile, bus, truck and the like.
FIGS. 1 and 2 illustrate a typical example of a conventional windshield wiper device W which is used for wiping the front window glass, i.e., the windshield of an automobile. This wiper device W includes: an arm head 5; a retainer 6 pivotally connected at its proximal end to the arm head 5 for right and left movement as viewed in FIG. 1; an arm spring 7 interconnecting the retainer 6 with the arm head 5 so as to urge the retainer 6 to the right; and an elongated wiper blade 4 connected to the distal end of the retainer 6 so as to extend substantially parallel to the retainer 6. Such a wiper device W is adapted to be mounted on the automobile M as shown in FIG. 2 and to be oscillated, for example, in tandem manner along the outer surface of the windshield 3. More specifically, the arm head 5 is to be fixedly connected to a wiper shaft 1 below the windshield 3 in such a manner that the wiper blade 4 is pressed against the outer surface of the windshield 3 by the arm spring 7. The wiper shaft 1 is drivingly connected through a linkage to an electric motor (not shown) which is installed in the automobile M, and thereby, when the motor is turned on, the wiper device W is oscillated so that the wiper blade 4 squeegees an area A of the windshield 3 shown by the phantom line in FIG. 2. In the case that the outer surface of the windshield 3 is convexly curved as shown in FIG. 3 or slanted to a plane perpendicular to the longitudinal axis of the automobile M, the retainer 6 is pivoted about its pivot shaft 6a during the oscillation of the wiper device W. Therefore, the entire wiper blade 4 is constantly kept in contact with the outer surface of the windshield 3.
However, when the curvature of the windshield's outer surface exceeds a predetermined value, there arises a problem during the oscillation of the wiper blade 4, of the angle .alpha. between the centerline Cb of the wiper blade's cross section and the tangent line L to that point on the windshield 3 which the wiper blade 4 contacts, being increased or decreased to a value inconveniently far from the ideal angle of 90.degree. (see phantom line in FIG. 3). As a result, the wiper blade 4 neither smoothly oscillates along the windshield 3 nor effectively squeegees the windshield 3, and furthermore, a chattering noise is occasionally generated due to the unsmooth oscillation of the wiper blade 4. Such a problem tends to be aggravated by both the diversification of modern vehicles' designs and the improvements made in the aerodynamical characteristics of modern vehicles. In addition, the difference .DELTA..alpha. between the angle .alpha. and the ideal angle is called the error angle. The maximum permissible error angle of a wiper blade varies depending on both the elastic modulus of the arm spring and the material and shape of the wiper blade, however, it is, generally, about 8.degree..